The present invention relates generally to a process for coating at least one surface of a substrate made of transparent organic glass which improves the adhesion of the coating to the substrate.
It is conventional, in the field of ophthalmic optics, to coat the surfaces of a substrate made of organic glass, such as an ophthalmic lens made of organic glass, for example a spectacle lens, with coatings such as hard abrasion-resistant and/or impact-resistant coatings, in order to improve the resistance of the ophthalmic lens obtained to scratches and to impacts.
A problem associated with these coated substrates made of organic glass relates to the adhesion of the coating to the substrate.
It would therefore be desirable to develop a process for coating a substrate made of organic glass which improves the adhesion of the coating to the organic glass and which can be applied to a large number of substrates made of organic glass where the substrates are different in nature.
The above aim is achieved according to the invention by providing a process for coating at least one surface of a substrate made of organic glass, such as an ophthalmic lens, for example a spectacle lens, which comprises, prior to the deposition of the coating on the surface of the substrate, a treatment stage comprising bringing the surface of the substrate into contact with an aqueous treatment solution comprising at least one surface-active agent.
In a recommended implementation of the invention, the stage of treatment with the aqueous solution of surface-active agent is followed by a stage of treatment of the surface with a basic solution, for example a 5% aqueous sodium hydroxide solution.
The process of the invention can also comprise, prior to the stage of treatment with the aqueous surfactant solution, a stage of treatment with plasma, in particular a conventional oxygen plasma. The use of such a stage of treatment with plasma of the substrate made of organic glass proves to be particularly advantageous when the organic glass of the substrate is a glass based on acrylic polymer.
For these organic polymers, the increase in the temperature of the treatment solution makes it possible appreciably to increase the adhesion of the coating. In particular, when the temperature of the solution is greater than or equal to 70xc2x0 C., an excellent adhesion of the coating is obtained without involving a stage of treatment with plasma.
Very clearly, the coating process can comprise, between the various treatment stages, stages of cleaning with an alcohol and of rinsing with deionized water. In particular, it is recommended, subsequent to the stage of treatment with the solution comprising the surface-active agent and prior to the stage of treatment with the basic solution, to carry out a rinsing stage, preferably rinsing with deionized water, in order to remove the excess solution comprising the surface-active agent.
In general, during the stage of treatment with the aqueous solution of surface-active agent, the substrate is brought into contact with the solution for a period of 1 to 5 minutes, preferably at temperatures of the order of 30 to 90xc2x0 C. and better still 40 to 60xc2x0 C. The stage of treatment with the aqueous solution of surface-active agent is preferably carried out while concomitantly applying an ultrasound treatment.
In another recommended implementation of the invention, the aqueous treatment solution comprising the surface-active agent comprises dispersed pigments and thus also constitutes a bath for colouring the substrates, in particular ophthalmic lenses. In this case, the treatment is carried out at temperature of approximately 90xc2x0 C. An excellent adhesion of a coating deposited subsequently on a coloured substrate (lens) is thus obtained. This technique exhibits two main advantages. On the one hand, it makes it possible to carry out, in a single stage, the colouring and the surface treatment for the adhesion and, on the other hand, it makes it possible to obtain an excellent adhesion of the coating even if the presence of pigments incorporated at the surface of the substrate has a tendency to degrade the properties of adhesion of the coatings.
The surface-active agents of use in the aqueous treatment solutions according to the invention can be any known surface-active agent and preferably anionic or nonionic surface-active agents.
Mention may be made, among surface-active agents recommended for the treatment solutions according to the invention, of alkyl sulphates, alkyl ether sulphates, alcoholamine alkyl sulphates, alkyl-benzenesulphonates and poly(ethylene glycol) alkylphenyl ethers.
Surface-active agents which are particularly recommended in the aqueous treatment solutions according to the invention are sodium lauryl sulphate (NaLS), sodium lauryl ether sulphate (NaLES), triethanolamine lauryl sulphate (TEALS), sodium dodecylbenzenesulphonate (NaDDBS) and PEG-9 octylphenyl ether (TRITON(copyright) X 100).
A surface-active agent which is particularly recommended according to the invention is sodium lauryl ether sulphate (NaLES).
The surface-active agent or agents present in the solution generally represent 0.01 to 0.1%, preferably 0.05 to 0.1%, by weight with respect to the total weight of the aqueous treatment solution.
The preferred aqueous treatment solutions according to the invention also comprise a hydrophilic polymer or colloidal hydrophilic inorganic filler or a mixture of these.
Mention may be made, among hydrophilic polymers recommended in the treatment solutions according to the invention, of poly(vinyl alcohol)s (PVA), poly(ethylene glycol)s (PEG), polyacrylamides (PAM), polyvinyl-pyrrolidones (PVP) and cellulose derivatives, such as hydroxy alkyl celluloses, such as hydroxy ethyl cellulose and hydroxy propyl cellulose, alkyl hydroxy alkyl celluloses, such as methyl hydroxy propyl cellulose, and carboxy alkyl celluloses, such as carboxy methyl cellulose.
Mention may be made, among hydrophilic colloidal inorganic fillers suitable in the aqueous treatment solutions according to the invention, of silica fillers, alumina fillers and their mixtures, in particular pyrogenic silica and alumina fillers.
The hydrophilic polymer or polymers and/or the hydrophilic colloidal inorganic fillers are generally present in the aqueous treatment solution according to the invention in a proportion of 0.001 to 0.05%, preferably 0.005 to 0.02%, by weight with respect to the total weight of the aqueous treatment solution.
Aqueous treatment solutions which are recommended according to the invention are solutions which comprise an anionic surfactant and a hydrophilic polymer and/or a nonionic or cationic colloidal inorganic filler.
Aqueous treatment solutions according to the invention which are particularly preferred additionally comprise a hydroxylamine salt and/or a hydrazine salt, such as, for example, hydroxylamine hydrochloride and/or hydrazine hydrochloride.
When it is present, this hydrazine or hydroxylamine salt represents 0.02 to 0.1% by weight with respect to the total weight of the aqueous treatment solution.
Preferably again, the aqueous treatment solutions according to the invention have an acidic pH, generally from 2 to 5. This acidic pH can be obtained by addition of an acid, preferably lactic acid, to the solution, if necessary.
The amount of lactic acid present in the aqueous treatment solution generally represents 0 to 0.01% by weight with respect to the total weight of the aqueous treatment solution.
The present invention thus also relates to an aqueous treatment solution for the implementation of the process of the invention which comprises a surface-active agent, a hydrophilic polymer and/or a hydrophilic colloidal inorganic filler, a hydrazine salt and/or a hydroxylamine salt, and an acid.
An aqueous treatment solution which is preferred according to the invention comprises (the % being expressed by weight with respect to the total weight of the aqueous treatment solution):
0.01 to 0.1% of at least one surface-active agent;
0.001 to 0.05% of a hydrophilic polymer and/or of a hydrophilic colloidal inorganic filler;
0.02 to 0.1% of a hydrazine salt and/or a hydroxylamine salt; and
up to 0.01% of acid, preferably lactic acid.
The substrates made of organic glass which can be treated in the process of the invention are all substrates made of transparent organic glass for which it is necessary to improve the surface condition for the purpose of facilitating the subsequent adhesion of a treatment and in particular of an abrasion-resistant coating.
Mention may be made, among these substrates, of substrates based on (meth)allyl polymer, substrates based on (meth)acrylic polymer, substrates based on thio(meth)acrylic polymer, substrates based on poly(thio)urethane and substrates based on thermoplastic polycarbonate.
The preferred substrates are of (meth)allyl, (meth)acrylic and poly(thio)urethane type.
A first family of substrates is composed of those obtained from polymerizable compositions comprising (meth)allyl monomers or prepolymers derived from bisphenol A, in particular bisphenol A bis(allyl carbonate).
The latter can be used alone or as a mixture with other copolymerizable monomers, in particular with di(ethylene glycol) bis(allyl carbonate).
Substrates which are more particularly recommended, as well as their process of preparation, appear in the Patent Documents EP 224,123 and FR 2,703,056.
A second family of substrates is composed of those obtained from polymerizable compositions comprising (meth)acrylic monomers or prepolymers derived from bisphenol A, in particular bisphenol A dimethacrylate or poly(ethoxy)bisphenol A dimethacrylate.
Such substates are disclosed, inter alia, in Patent EP 605,293.
A third family of substrates is composed of those obtained from compositions including at least one polythiol compound and at least one polyisocyanate compound which result in a polythiourethane substrate.
Such substrates, as well as their process of preparation, are disclosed more particularly in U.S. Pat. Nos. 4,689,387 and 4,775,733.
To facilitate the release of such substrates from a mould, it is possible to incorporate internal mould-release agents.
Such agents are disclosed in Patent EP 271,839.
The preferred mould-release agents are hydrogen phosphates, such as dibutyl phosphate.
The consequence of the presence of the internal mould-release agent is a decrease in the adhesion of the treatments, in particular of the coatings, subsequently deposited on the substrate.
The invention is therefore of particular advantage in the case of substrates comprising such mould-release agents.
A fourth family is that composed of polycarbonate materials (thermoplastics).
The coatings which can be deposited on the substrates made of organic glass pretreated according to the invention are all coatings conventionally used in the field of ophthalmic optics, such as hard abrasion-resistant and/or impact-resistant coatings.
Mention may be made, among abrasion-resistant coatings recommended in the present invention, of coatings obtained from compositions based on silane hydrolysate, in particular on epoxysilane hydrolysate, for example those disclosed in Patent EP 0,614,957, or from the compositions based on (meth)acrylic derivatives.
An abrasion-resistant coating composition which is particularly recommended in the process according to the invention is a composition comprising a xcex3-glycidoxypropyltrimethoxysilane hydrolysate, optionally a dimethyldiethoxysilane hydrolysate, colloidal silica and aluminium acetylacetonate.
Another coating which can be envisaged is a coating based on polyurethane, in particular polyurethane latex.
The deposition of the coating on the surface of the substrate made of organic glass, which surface is treated according to the invention, is carried out conventionally by application of a solution of the coating composition and then conventional hardening of this composition.
The process according to the invention generally makes it possible to obtain an excellent adhesion of the coatings subsequently deposited on the pretreated substrate made of organic material and in particular coatings themselves made of organic material.
The process makes it possible to avoid any mechanical surface brightening treatment which will be harmful to the transparency.
In addition, it results in coated substrates, in particular ophthalmic lenses, having an excellent cosmetic appearance.